Isoprenoids are a large and structurally diverse group of compounds that play essential roles in plants as hormones, photosynthetic pigments, electron carriers, and components of membranes, and that also serve in communication and defense (Harborne, J. B. (1991) in Ecological Chemistry and Biochemistry of Plant Terpenoids (Harborne, J. B., and Tomas-Barberan, R. A., Eds.), pp. 399-426. Clarendon Press, Oxford). Until recently, it was widely accepted that all isoprenoids were synthesized via the acetate/mevalonate pathway (Spurgeon. S. L., and Porter, J. W. (1983) in Biosynthesis of Isoprenoid Compounds (Porter, J. W., and Spurgeon, S. L., Eds.), Vol. 1, pp. 1-46, John Wiley, New York).
However, evidence has emerged over the last few years that isopentenyl diphosphate, the central intermediate of isoprenoid biosynthesis, originates from pyruvate and D-glyceraldehyde-3-phosphate via a new mevalonate-independent pathway in several eubacteria (Rohmer, M., et al., Biochem. J. 295, 517-524 (1993); Broers, S. T. J. (1994) Ph.D. Thesis, Eidgenossische Technische Hochschule, Zuirich, Switzerland; Rohmer, M., et al., J. Am. Chem. Soc. 118, 2564-2566 (1996)), algae (Schwender, J., et al., Biochem. J. 316, 73-80 (1996)), and plant plastids (Schwarz, M. K. (1994) Ph.D. Thesis, Eidgenossische Technische Hochschule, Zurich, Switzerland; Lichtenthaler, H. K., et al., FFBS Lett. 400, 271-274 (1997)). The first step in this novel pathway involves a transketolase-type condensation reaction of pyruvate and glyceraldehyde-3-phosphate to yield 1-deoxy-D-xylulose-5-phosphate (FIG. 1). Genes encoding the enzyme which catalyzes this reaction, deoxyxylulose phosphate synthase, have been cloned from E. coli (Sprenger, G. A., et al., Proc. Natl. Acad. Sci. USA 94, 12857-12862 (1997); Lois, L. M. et al., Proc. Natl. Acad. Sci. USA 95, 2105-2110 (1998)), peppermint (Mentha x piperita) (Lange, B. M. et al., Proc. Natl. Acad. Sci. USA 95, 2100-2104 (1998)) and pepper (Bouvier, F. et al., Plant Physiol. 117,1423-1431 (1998)).
The second step of the mevalonate-independent pathway is considered to involve an intramolecular rearrangement and subsequent reduction of deoxyxylulose phosphate to yield 2-C-methyl-D-erythritol-4-phosphate (Duvold, T. et al., Tetrahedron Lett. 38, 4769-4772 (1997); Duvold, T. et al., Tetrahedron Lett. 38, 6181-6184 (1997); Sagner, S. et al., Tetrahedron Lett. 39, 2091-2094 (1998)) (FIG. 1). Seto and coworkers (Takahashi, S. et al., Proc. Natl. Acad. Sci. USA 95, 9879-9884 (1998)) have recently reported the isolation and characterization of a reductoisomerase gene from E. coli. The present invention provides a nucleic acid molecule isolated from peppermint that encodes a 1-deoxy-D-xylulose-5-phosphate reductoisomerase.